Photoelectric device



IMay 7., 1935. A. H.' LAMB 0 Y 2,000,642

PHOTOELECTRIC DEVCE Filed July 14. 1932 'Patented May 1, 193sv UNITEDSTATES y amsn ruo'romc'rmc nevica Anthony n. Lamb, Elisabeth, N. '.r.,signor o Weston Electrical Instrument Corporation, Newark, N. J., acorporation of New JerseyY Application July 14, 1932, Serial No. 622,531

type including an actinoelectric material such as cuprous oxide,solenlum, tellurium, selenides, tel- -lurides and the'like.

Photoelectricycells of this type have been designed and used ascurrent-change devices for the operation, either directly or throughamplifiers, of current-response devices since, in general,

the maximum voltage generated is too low to actuate satisfactorily astatic amplifier, or to actuate directly a dynamic amplifier. Photocellsof the'evacuated tube type are essentially voltagechange devices ln thatthe current output is so minute as to be of no practical use, vwhereasthe voltage change resulting from wide variations in illumination is ofsubstantial magnitude. The phototubes are not, however, sensitive tosmall changes within the range` of relatively low illumination.

An object of the -invention is toprovide photoelectric devices of thevoltage-change type, and which are characterized bya higher sensitivitythan the .known phototubes. A further object is to provide photoelectricdevices of high voltage output, and of the type including a layer ofactinoelectric material disposed between two electrode terminals. A

These and other objects and advantages of the invention will be apparentfrom the following spec'fication, when taken with the accompanying ydrawing, in which:

Fig. l is a somewhat diagrammatic sectional view of a photocell of thecurrent generating type,

Fig. 2 is a diagram oi.' a' circuit including a plurality of such cells,

, Fig. 3 is a plan view of a device embodying the invention,

Fig. 4 is a sectional view on line 4-4 of Fig. 3, and

' Figs.'5 to' 8, inclusive, are somewhat diagrammatic plan views ofother mountings for cascaded cell units.

In the drawing, the reference numeral I ident'fles the actinoelectriclayer of material that is arranged between a collector or grid electrode2 and a second electrode 3 to forma photoeleetric cell CI The layerllmay consist of selenium that was applied'in molten state to the backingelectrode 3, and then heat treated to produce a crystalline structure.The collector electrode 2 is shown as a. grid with relatively largeopenings but it is to be understood that this showing serves only forpurpose of illustration as the collecting electrode may have other knownforms, that of a translucent film of metal.

Whether the actinoelectric layer be crystalline selenium or one of theother materials noted above, a photo-electric device such as shown 1nFig. 1 has the property of generating a voltage between the electrodes2, 3 when.the collecting electrode face of the layer i is exposed tolight and its opposite face is dark. 'I'he voltage so developed is 'of avery low order of magnitude but 10 a substantial ilow of current may beestablished in an external circuit between the electrodes. l Theabsolute values of the voltage and current .will be diierent, of course,for the diiferent actinoelectric materials, the collecting'electrodecon- 15 struction and the intensity of the illumination but in all casesthe action will be of the type indicated graphically in Fig. l. Ifappropriate voltage and current measuring instruments are employedfasindicated diagrammatically by instruments V and A, respectively, it willbe found that -the maximum voltage obtainable under strong illuminationis quite small but the current output is appreciable. In view of thischaracteristic of the devices, they have been uniformly employedwithauxiliary equipment that respondcd to changes in current flow.

As indicative of the low voltages developed, it has been impossible toobtain potentials greater than from '75 to 150 millivolts as therelatively rapid variation in voltage which results from variations inrelatively low illumination does not extend over the entire range ofillumination, a saturation effect preventing any increase in voltagewith increasing illumination.

Voltages of the order stated are ltoo low to operate satisfactorilythevoltage-response devices that are employed with photo-electric devicesof the vacuum tube type.

I have discovered that cells of the currentchange type may be cascadedto develop a voltage, when working into a circuit of suchhighlresistance as to substantially prevent all current flow, that issubstantially the sum of the voltages developed by the individual cells,and that the size of the cascaded cells may be but fa smallfraction ofthe size of the cells commonlyfformed of the same materials and for useas currentchange devices. Thecurrent output of currentchange cells ofthe solid type is dependent upon the exposed area of the cell but I havefound that the desired voltage 'addition effect may be obtained by'cascading a plurality of current-change cell units which are each ofsuch small size as to develop only a negligible current.

such asv light or to open .As shown in Fig. 2, a plurality oi' cells Cmay be cascaded by connecting the collecting electrode of one cell tothe back electrode of the adjacent cell. The terminals of the cascadedcells may be connected to a thermiomc amplifier 4 or other voltageresponse device, the number of cells being so chosen that the voltagedeveloped between the terminals is suilicient to actuate the amplifier.as indicated graphically by the measuring instruments V, A, in Fig. 2,the input resistance oi the amplifier is ao high that there is nocurrent iiow. but the open-circuit voitage produced upon enh posing thecells to iight is relatively high. The

open-circuit voltage ci the cascaded cells cannot be measured by (asensitive millivoltmeter connected ...cross the terminals, since theinstrument winding will short-circuit the cells and the voltage williall appronimately to zero, and it is to be understood that the showingof the voltmeter V indicates only the magnitude of the open-circuitvoltage, and not a circuit for measuring that voltage. With ten cascadedcells, for example, over 30u millivolts were developed at 5 footcandlesand over lVZ volts were developed at 25u foot-candles. The highmillivolt sensitivity at low illumination is thus rendered available forcontrol purposes as the absolute value of the voltage changecorresponding to a given change in illumination may be stepped up to anydesired magnitude by choice ofthe number of cascaded cells.

One practical arrangement for a device comprising a plurality ofcascaded cells is shown in Figs. 3 and 4. An'insulating base 5 isrecessed to provide seats for receiving a plurality of small cells C andthe lower ends of approximately Z-shaped connecting strips 6; the upperends of the strips overlying an adjacent recess, whereby the strips makecontact between the collecting electrode of one next cell. A glass coverplate l is secured to the b'ase 5 by a screw 0 and holds the outer endsof the connecting strips 6 in contact with the respective collectingelectrodes. Terminal strips 9 extend from opposite faces of the two endcellsr to points beyond the base i5.

It is to be noted that the size oi' a multiple cell potential-generatingdevice is not directly related to the size of the knowncurrent-generating cells employing the same materials. The individualcell units C' may be, and preferably are, quite small and the dimensionsand shape of the complete multi-cell device may be the same as those ofa single cell C of the current-change type, thus facilitating themanufacture ci mountings and auxiliary equipment by one constructionavailable for use with cells of both the voltage-change and thecurrent-change types.

It will be apparent that there is considerable latitude in the choice ofthe materials of the individual cell umts, and in the physicalarrangements of the cascaded cells.

As illustrated in Fig. 5, a plurality of individual' cells C are alinedand carried by a narrow strip I of insulating material. This form ofmounting is particularly desirable when a comparatively extended regionis to be protected by a light-sensitive alarm or control system. The`for example, be mounted along" strip Il may, the side of an elevatordoor to energize a signal a circuit-breaker when any object cell and thebase electrode of the -is in such position as to be injured by closingthe door or starting the elevator.

The mounting plate i I may be oi annular form, as shown in Fig. 6, or acircular mounting I2 may support s plurality oi unit cells C2 which areof sector shape. Or. as shown in Fig. 8, a plurality oi unit cells C"may be compactly arranged on a square mounting plate iii.

The number oi cascadcd cells and their arrangement muy, ofcourse, bevaried to suit the particular design requirements in any given case.

I claim:

l. A photoclectric device of the voltagechange type comprising a base ciinsulating material having recesses in one face thereoi, acurrent-generating photoelectric celi snugly received within each oisaid recesses, each ci said cells being of disk form and comprising alayer of actinoelectric material between a baci: electrode and an upperlight-transmitting electrode, conducting strips connecting said cells incascade, each strip having an end extending,r to the bottom oi onerecess and an opposite end overlying the upper electrode oi a cell in anadjacent recess, a glass plate overlying said cella and connectingstrips, and means clamping said plate to said base to retain said stripsin electrical contact with the several cells.

2. A photoelectric device as .claimed in claim 1, wherein theactinoelectric material of said cells is selenium, whereby said cellshave a high resistance when not illuminated.

3. A photoelectric device of the voltagechange type comprising a base ofinsulating material, a plurality of connecting strips on said base andeach having an outer end overlying and spaced from the inner end of anadjacent strip, a photoelectric cell unit of the current-generating typebetween each set of opposed inner and outer ends of adjacent strips,each cell unit comprising a layer of actinoelectric material between aback electrode and an upper light-transmitting electrode, and meanssecuring said cells to said base and retaining the respective ends ofsaid strip in electrical contact with the cell electrodes adjacentthereto.

fi. A photoelectric device as claimed in claim 3, wherein each cell unitis below the size capable oi developing an appreciable current output.

5. A photoelectric device of the voltage-change type comprising arecessed base of insulating material, a plurality ot photoelectric cellunits of the current-generating type mounted on said base and with theouter surface thereof substantially flush with the surface of said base,each cell unit comprising a layer of actinoelectric material between andunited to a back electrode and an outer light-transmitting electrode, apair oi terminals electrically connected to electrodes oidlierent types`oi' two of said cell umts, a plurality of conducting membersvconnecting the said cell units in cascade between the said pair ofterminals, each connecting member having one outer end overlying thelight-.transmitting electrode of one cell unit and an inner end incontact with the back electrode of an adjacent cell unit, and meanssecuring said cell umts to said base and retaining said connectingmembers in electrical contact with their associated cell unitelectrodes.

